1. Technical Field
The invention relates to apparatus and method for measuring cavitation energy profiles on devices placed in ultrasonic and megasonic cleaning systems.
2. Field of the Invention
Ultrasonic and megasonic cleaning systems are well known and are used in a wide variety of applications to clean various types of devices. Typically, a cleaning system has a tank with a cleaning bath that may consist of water with a cleaning material such as a detergent recommended and selected for use in cleaning particular types of devices. Ultrasonic and megasonic systems, sometimes referred to as agitation systems, have a transducer designed to generate high frequency vibrations in the cleaning tank in response to an electric input top the transducer. An ultrasonic cleaning system may operate in a range of 20 kHz to 400 kHz while a megasonic system may operate in a range of 500 kHz to 3 MHz.
In operation, the transducer vibrations are introduced into the cleaning tank containing the bath and the device or devices to be cleaned. The introduced vibrations generate pressure gradients within the bath, which form cavitation bubbles in low-pressure areas. The bubbles begin to grow until entering a high-pressure region and then collapse against a surface of the device to be cleaned thereby dislodging contaminants. The implosion of the bubbles creates a strong force over a period of time to clean devices such as memory disks, semiconductor wafers, LCD and other like devices.
Ultrasonic energy is a series of pressure points, or rather a series of compression and rarefaction. If the energy is of sufficient intensity, the cleaning liquid of the bath will actually be pulled apart and small bubbles or cavities will be formed. The bubbles collapse or implode throughout the cleaning fluid creating an effective force, which is uniquely suited to cleaning. This process is known as cavitation. Although the energy released from a single cavitation bubble is extremely small, the collapse of millions of bubbles produces an intense scrubbing action of the surface of the device to be cleaned. In many cleaning processes the control of cavitation energy is one of the most critical parameters affecting product yield. A problem arises in that if not enough energy is present on a surface location, the device will not be cleaned. Another problem arises in that if too much energy is present in one location the excessive force may damage the device being cleaned. One method of measuring cavitation is an indirect method that consists of exposing aluminum foil to the cavitation process and then examining the foil for dents and holes caused by the cavitation process. The current technology is limited to the measurement of the ultrasonic sound waves energy by the use of instructions called hydrophones. A problem with hydrophones systems arises in that they are limited to detecting only very low frequencies typically in the range of 40 kHz to 68 kHz. Thus, hydrophone systems act as a low-pass filter, which automatically filters out and removes the higher frequency cavitation energy. Neither of these methods measure the cavitation process at various locations within the cleaning bath. Accordingly, a need exists in the art for apparatus and a method for actively measuring the cavitation process at various locations in the cleaning bath during operation of removing contaminants from devices placed in the bath.
Apparatus solves the foregoing problem by measuring the cavitation process at various locations in a cleaning bath during ultrasonic and megasonic sonic cleaning of devices placed in the cleaning bath.
It is an object of this invention to provide apparatus for measuring the cavitation activity occurring in various locations in an ultrasonic and megasonic cleaning bath and for generating a profile of the cavitation process occurring at various locations on the surface of a device resident in the cleaning bath.
It is also an additional object of this invention to provide probe apparatus having a plurality of probe sensors for measuring cavitation energy appearing at various locations in an ultrasonic and megasonic cleaning bath.
It is also an additional object of this invention to provide apparatus coupled to each probe of the probe array immersed in an ultrasonic and megasonic cleaning bath for analyzing the voltage waveform generated by each probe and determining a cavitation energy profile occurring on surfaces of a device located in the bath.
In the preferred embodiment of the invention apparatus for measuring cavitation energy of a bath resident in a tank of ultrasonic and megasonic cleaning systems has probe apparatus having an array of probes positioned within the bath for detecting the pressure formed by the collapse of bubbles at various locations within the bath that are generated by ultrasonic and megasonic vibrations applied to the bath and with each probe of the array generating an electrical waveform in response to the detection of the bubbles. Apparatus coupled to each probe of the probe array analyzes the voltage generated each probe and determines a cavitation energy profile occurring on surfaces of a device located in the bath.